GalileoDecember 7, 1995

After a five-year voyage, the Galileo spacecraft
arrives at Jupiter. Still in orbit in 2002, it has made more than
30 orbits of Jupiter, usually flying close to one of its four major
moons.

Through its observations, Galileo scientists
discover strong evidence that Jupiter's moon Europa has a melted
saltwater ocean under an ice layer on its surface. The spacecraft
also finds indications that two other moons, Ganymede and Callisto,
have layers of liquid saltwater as well.